Linear alkylbenzene sulfonate (LAS) is one of the most widely used surfactants in commerce. It finds special application for light and heavy duty liquid and powder detergents. A potential disadvantage of LAS, however, is that under hard water conditions, i.e., calcium levels greater than about 150 parts per million, it can interact with cationic water hardness ions, such as calcium, thereby becoming inactivated through precipitation. While this is a problem common to anionic surfactants, LAS is especially sensitive to water hardness ions.
Although not wishing to be bound by any theory, the literature indicates that the aforementioned interaction can best be understood by considering the micellar structure of anionic surfactants, e.g., LAS. Repulsive forces between negative charges in the sulfonate group lead to a higher critical micelle concentration (CMC) than, for example, with a nonionic surfactant. CMC is the surfactant concentration at which micellar formation begins. Stated otherwise, the negative charge of LAS retards micellar formation and shifts the equilibrium towards the monomer. A relatively high monomer concentration in solution results thereby; this is significant because precipitation between calcium ion and LAS occurs only with the monomer.
It has been found that detergent formulations containing a surfactant composition comprising one or more nonionic surfactant components and one or more secondary alkyl sulfate compounds as anionic surfactant components can be used in various detergent formulations in place of either linear alkylbenzene sulfonate or primary alkyl sulfates with the advantages being increased tolerance for water hardness ions, good detergency properties, biodegradability, higher active matter content, lower water content, lighter color and good foaming properties.